The utilization of water which contains certain inorganic impurities, and the production and processing of crude oil water mixtures containing such impurities, is plagued by the precipitation of these impurities with subsequent scale formation. In the case of water which contains these contaminants the harmful effects of scale formation are generally confined to the reduction of the capacity or bore of receptacles and conduits employed to store and convey the contaminated water. In the case of conduits, the impedance of flow is an obvious consequence. However, a number of equally consequential problems are realized in specific utilizations of contaminated water. For example scale formed upon the surfaces of storage vessels and conveying lines for process water may break loose and these large masses of deposit are entrained in and conveyed by the process water to damage and clog equipment through which the water is passed. e.g., tubes, valves, filters and screens. In addition, these crystalline deposits may appear in and detract from, the final product which is derived from the process, e.g., paper formed from an aqueous suspension of pulp. Furthermore, when the contaminated water is involved in a heat exchange process, as either the "hot" or "cold" medium, scale will be formed upon the heat exchange surfaces which are contacted by the water. Such scale formation forms an insulating or thermal opacifying barrier which impairs heat transfer efficiency as well as impeding flow through the system.
Scale can also be formed during evaporative cooling, when the level of dissolved ionic species will increase as water from the solution evaporates. Scale will then form when the concentration of a salt exceeds its solubility under the conditions experienced. This scaling process is typically observed in evaporative cooling towers, and the buildup of scale on the tower fill can cause a large decrease in tower efficiency.
While calcium sulfate and calcium carbonate are primary contributors to scale formation, other salts of alkaline-earth metals and the aluminum silicates are also offenders, e.g., magnesium carbonate, barium sulfate, the aluminum silicates provided by silts of the bentonitic, illitic, and kaolinitic types among others. When phosphate anions are present, either naturally or added to the system, calcium phosphate scaling can also be significant.
Many other industrial waters, while not being scale forming, tend to be corrosive. Such waters, when in contact with a variety of metal surfaces such as ferrous metals, aluminum, copper and its alloys, tend to corrode one or more of such metals or alloys. A variety of compounds have been suggested to alleviate these problems. Such materials are low molecular weight polyacrylic acid polymers. Corrosive waters of this type are usually acidic in pH and are commonly found in closed recirculating systems.
Numerous compounds have been added to these industrial waters in an attempt to prevent or reduce scale and corrosion. One such class of materials are the well known organophosphonates which are illustrated by the compounds hydroxyethylidene diphosphonic acid (HEDP) and phosphonobutane tricarboxylic acid (PBTC). Another group of active scale and corrosion inhibitors are the monosodium phosphinicobis (succinic acids) which are described in U.S. Pat. No. 4,088,678. Further, N,N-bis(phosphono methyl) derivative compounds in combination with homo or copolymers are disclosed for inhibition of calcium carbonate deposition in U.S. Pat. No. 5,087,376.
Most industrial waters contain alkaline earth metal cations, such as calcium, barium, magnesium, etc. and several anions such as bicarbonate, carbonate, sulfate, oxalate, phosphate, silicate, fluoride, etc. When combinations of these anions and cations are present in concentrations which exceed the solubility of their reaction products, precipitates form until these product solubility concentrations are no longer exceeded. For example, when the concentrations of calcium ion and carbonate ion exceed the solubility of the calcium carbonate reaction products, a solid phase of calcium carbonate will form. Calcium carbonate is the most common form of scale in many industrial processes.
Solubility product concentrations are exceeded for various reasons, such as partial evaporation of the water phase, change in pH, pressure or temperature, and the introduction of additional ions which form insoluble compounds with the ions already present in the solution.
As these reaction products precipitate on surfaces of the water carrying system, they form scale or deposits. This accumulation prevents effective heat transfer, interferes with fluid flow, facilitates corrosive processes and harbors bacteria. This scale is an expensive problem in many industrial water systems causing delays and shutdowns for cleaning and removal.
Scale deposits are generated and extended principally by means of crystal growth; and various approaches to reducing scale development have accordingly included inhibition of crystal growth, modification of crystal growth and dispersion of the scale-forming minerals.
Various polymeric treatments for scale control exist Among them are the use of anionic co- or ter-polymers of N-vinyl-2-pyrrolidone or vinyl amide, as disclosed in U.S. Pat. No. 4,913,824; the use of maleic anhydride/quaternary ammonium-type polymers as disclosed in U.S. Pat. No. 5,015,390 and the use of co- and ter-polymers of (meth)acrylic acid and sulfoalkyl(meth) acrylamide as disclosed in U.S. Pat. No. 4,801,388.
Co-polymerization of N-(4-sulfoalkyl)N-methyldiallyl ammonium betaines with N-vinyl pyrrolidone or acrylamide to obtain a water-soluble co-polymer has been disclosed in U. S. Pat. No. 4,585,846.
However, there is still a need for a polymeric treatment to more efficiently combat scale. The polymers described herein accomplish this purpose.